oracle存储过程中动态执行SQL

vs_sql := 'select object_value from '|| vs_table
      ||' where city_code = :is_citycode'
      ||' and service_kind = :in_service_kind'
      ||' and object_id = :in_id'
      ||' and object_control = 1';

  begin
    execute immediate vs_sql into on_value using is_citycode,in_service_kind,in_id;